The present invention relates to a cell relay communication method, cell relay communication system and cell relay communication equipment for relaying compressed voice data wherein the delay time caused by the communication relay is shortened in a communication network comprising of a plurality of transmission devices connected to an ATM network.
The system structure of a prior art cell relay network communicated through an ATM network is explained with reference to FIG. 9.
The relay network is formed by connecting a plurality of transmission devices 10a through 10c of a private branch exchange (hereinafter called PBX) having a voice relay function and a call transmission/reception control function or a multiplexing device (hereinafter called TDM) each storing extension telephones 40 and the like to an ATM network 20 through a cell assembly and disassembly device (hereinafter called CLAD device) having a function of assembling and disassembling cells.
Each CLAD device 30a through 30c comprises a function to disassemble the cells received from the ATM network 20 into bit-strings of digital data having a fixed communication speed such as voice communication, to transfer the same to the transmission device, and to assemble the digital data bit-strings received from the transmission device into cells and transmit the same to the ATM network 20.
In a cell relay network having the above-mentioned structure, for example, the analog voice data [AD] from the telephone 40a is converted to digital data bit-strings [DD] at the transmission device 10a, and then transferred to the CLAD device 30a. The CLAD device 30a assembles the transferred digital data bit-strings into cells [ATM cell] for multiplexing, and transmits the cells to the corresponding CLAD device 30b through the ATM network 20.
At the corresponding CLAD device 30b, the multiplexed cells are disassembled to receive the cells locally-addressed to said device 30b, converts the cells into digital data bit-strings [DD] and transfers the same to the transmission device 10b. The transmission device 10b restores the digital data bit-strings to voice data [AD], and outputs the data to a telephone 40b. 
As disclosed, the transmission device 10 holds the function of transferring the cells transmitted thereto to other terminals, and a call transmission/reception control function for controlling the transmission or reception of calls from or to its own terminal.
That is, when taking the transmission device 10b as an example, the calls that will be handled by the transmission device 10b will include a locally-addressed call to its own terminal where a call channel is formed from a telephone 40a connected to the call generation side transmission device 10a through the transmission device 10a, the CLAD device 30a, the ATM network 20, the transmission device 10b, and the telephone 40b as shown by the arrow a-b, and will also include a relay call where the call channel is formed between the telephone 40a, the transmission device 10a, the CLAD device 30a, the ATM network 20, the CLAD device 30b, the transmission device 10b, the CLAD device 30b, the ATM network 20, the CLAD device 30c, the transmission device 10c, and the telephone 40c shown by the arrow a-c.
In a relay call, the CLAD device 30b converts the cells received from the ATM network 20 [ATM cells] to a low-speed voice compression data [DD], and transfers said data to the transmission device 10b, where the low-speed voice compression data [DD] is transferred to the relay channel, and the CLAD device 30b converts the data into cells [ATM cells] again and transfers said cells to the ATM network 20, for the data to be relayed to the transmission device 10c. 
In such relay method, there was a loss of time for the CLAD device 30b to receive the low-speed voice compression data [DD] from the transmission device 10b and to assemble the data into cells [ATM cells], which caused a delay time of the voice. For example, when the voice was compressed to 8 Kbps, it took 48 ms for the CLAD device 30b to receive the low-speed voice compression data [DD], which becomes the voice delay time.
The present invention aims at solving the above problems, and the object of the invention is to provide a relay system comprising a transmission device of PBX or TDM having a voice relay function and a call transmission/reception control function which is connected to an ATM network through a CLAD device, wherein the compressed voice data is relayed by high-speed transfer between the CLAD device and the transmission device, so as to shorten the delay time of the relay.
In order to solve the above problems, the present invention provides a cell relay communication method in a relay system comprising a transmission device having a voice relay function and a call transmission/reception control function connected to an ATM network through a cell assembly and disassembly device having a function of assembling and disassembling cells, wherein the method identifies whether a call received from the ATM network is a relay call or a locally-addressed call, and when said received call is a relay call, said received call is relayed by high-speed transfer through the transmission device, and when said received call is a locally-addressed call, said received call is transferred by compressed voice data speed to the transmission device.
Moreover, the present invention provides a cell relay communication method in a relay system comprising a transmission device having a voice relay function and a call transmission/reception control function connected to an ATM network through a cell assembly and disassembly device having a function of assembling and disassembling cells, wherein the method comprises between the transmission device and the cell assembly and disassembly device a relay call identification/indication function for identifying and displaying whether a call received from the ATM network is a relay call or a locally addressed call, and a transfer speed selection function for relaying the call by high-speed transfer through the transmission device when said received call is a relay call, and transferring the call by a compressed voice data speed to the transmission device when said received call is a locally addressed call, so as to shorten the delay time by relaying the call.
Moreover, the present invention provides a cell relay communication equipment to be used in a relay system comprising a transmission device having a voice relay function and a call transmission/reception control function connected to an ATM network through a cell assembly and disassembly device having a function of assembling and disassembling cells, wherein the equipment includes between the transmission device and the cell assembly and disassembly device a relay call identification/indication means for identifying and indicating whether a call received from the ATM network is a relay call or a locally addressed call, and a transfer speed selection means for relaying the call by high-speed transfer to the transmission device when said display of the relay call identification/indication means is a relay call, and for transferring the call by a compressed voice data speed to the transmission device when said display of the relay call identification/indication means is a locally addressed call.
According to the present invention, in a relay system comprising a transmission device having a relay function and a call transmission/reception control function connected to an ATM network through a cell assembly and disassembly device having a function for assembling and disassembling cells, the delay time of transmission in a relay call may be shortened by identifying and displaying whether the call received from the ATM network is a relay call or a locally addressed call, and by selecting the transfer mode according to the display by the transfer speed selection means.